In recent years, communication systems of a cellular scheme such as long time evolution (LTE) and worldwide interoperability for microwave access (WiMAX) have spread widely. Further, data traffic in the communication systems is increasing due to the spread of smartphones or the like. Accordingly, it is becoming increasingly important for each communication provider to increase a communication capacity of the communication systems.
It is also considered to utilize device-to-device (D2D) communication for offloading of data against the increase in the data traffic. For example, when two terminal apparatuses directly communicate with each other instead of communicating with each other via a base station, the data traffic of radio communication via the base station can be reduced to reduce a load of a network side including the base station.
For example, there has been disclosed technology that uses a radio terminal as a relay station for multihop communication, and assigns a radio resource (time slot) to the multihop communication (see, for example, JP 2004-248210A). Additionally, there has been disclosed technology that uses a radio terminal as a relay station for an ad-hoc network, and when it is determined that a data amount in the ad-hoc network has exceeded a transmittable data amount, allows the radio terminal to directly communicate with a base station (see, for example, JP 2009-89042A).